This invention relates to information storage equipment and more particularly to optical information storage equipment.
Different types of information can be digitally represent and stored on optically read discs. Compact Disc (CD) drives and Digital Versatile Disc (DVD) drive may be used to read the information from the discs. Examples of media that may be read using a CD or DVD drive are Compact Disc-Digital Audio (CD-DA), Compact Disc-Read Only Memory (CD-ROM), Compact Disc-Recordable (CD-R), Compact Disc-ReWritable (CD-R/RW and CD-RW), and Digital Versatile Disc-Read Only Memory (DVD-ROM). For more information on several forms of optical storage media refer to the Compact Disc Digital Audio Standard introduced by Philips and Sony, commonly known as xe2x80x9cthe Red Book,xe2x80x9d the Compact Disc Read-Only Memory Standard introduced by Philips and Sony, commonly known as xe2x80x9cthe Yellow Book,xe2x80x9d the CD-ROM/XA Standard introduced by Philips, Microsoft, and Sony, the Compact Disc Interactive (CD-I) Media Standard, commonly known as xe2x80x9cthe Green Book,xe2x80x9d ISO 9660, the Optical Storage Technology Association (OSTA) MultiRead Specifications for CD-ROM, CD-R, CD-R/RW, and DVD-ROM Devices, Revision 1.11, Oct. 23, 1997, all of which are expressly incorporated herein by reference.
In the early 1990""s CD-ROMs were operating at up to the quad-speed (4X) level. In 1998, it is not uncommon to find CD-ROM""s operating at 32X and beyond. As speeds have increased, challenges have arisen in the area of error detection and correction, as well as in other areas dependant on control of the CD sectors being serially transferred from the disc to the buffer. When problems relating to data read operations, error checking and control operations, or buffer error conditions occur, it is desirable to quickly and accurate restart the data transfer at the location last accessed. A correct solution should result in the buffer being filled with sequential sectors. There should be no skipped or duplicated sectors.
Currently existing solutions typically do not reposition the data read device at the exact position of the sector being processed when the error condition occurred. Instead, a reseek location is chosen that is several sectors before the sector being processed when the error condition occurred. This is an inefficient use of time, which has become increasingly important as optical storage device speeds have increased. A solution is needed that efficiently repositions the data read device to the location of the sector that was being processed when the error condition occurred.
In accordance with an illustrative embodiment of the present invention, problems associated with performing reseek operations in an optical storage device are addressed. In an illustrative embodiment, the present invention provides a use of shadow registers to store address information required to continue a data transfer from a CD or DVD. This allows for highly efficient firmware and short reseek times when recovering from nonconforming data read operations, nonconforming error checking or correction operations, or buffer full conditions, for example.
The correct address information to save in the shadow registers is determined by logic circuitry that takes into account the nature of the error condition, along with the specification of the sector being processed when the error condition occurred, to determine which address information will allow the being processed to be reread. The shadow registers save the address information of the sector currently being processed by the optical storage device. The microprocessor then can use the address information to reposition the data read device to a reseek location. Providing the needed address information in the shadow register allows for a highly efficient reseek to the optical storage medium in order to restart the transfer of data.
The foregoing and other features and advantages of an illustrative embodiment of the present invention will be more readily apparent from the following detailed description, which proceeds with references to the accompanying drawings.